Floating ring seal with return structures and process for making it

ABSTRACT

In order to return the fluid which has penetrated into the sealing gap of a floating ring seal, recesses with closed edges are machined inside the region permanently covered by the sealing surfaces in a sealing ring in which the fluid is drawn to an end of the recess very close to the chamber to be sealed and hydrodynamically taken to a high pressure. Mirror-image recesses are effective regardless of the direction of rotation. The recesses are machined in very small sliding surfaces of ceramic sealing rings using a laser beam. Such a floating ring seal has a relatively low leakage rate with low friction. Two fluids can be mutually sealed with a double recess array.

The invention relates to a sliding ring seal, in the end side sealingfaces of which there are made depressions, each depression having anendless edge within the region constantly covered by the sealing faces,the fluid which has penetrated between the sealing faces into thedepressions from the space to be sealed being entrained by the rotatingsliding face and both put under greater pressure and also brought asclose as possible to the space to be sealed, so that the fluid flowsback into the space to be sealed again, out of the depressions.

Generally, sliding ring seals seal a fluid (liquid or gas) by counteringthe fluid to be sealed with a high flow resistance produced by a verynarrow sealing gap between their end side sealing faces, as a result ofwhich the leakage flow penetrating through the gap is small. So that thesealing gap can always be kept very narrow during operation of a slidingring seal, the axially movable sealing ring is pressed against the othersealing ring both by means of springs and by the pressure of the fluidto be sealed. Although the fluid penetrates into the sealing gap undercapillary action, and possibly as a result of a difference in pressure,it can occur that the sealing faces touch one another in some regionstemporarily, thus become heated and wear. In order to preventdisadvantages resulting from this, namely the failure of the seal as aresult of overheating, fissure formation, decomposition of the fluid inthe sealing gap and the formation of deposits, excessive wear, etc.,there are in accordance with the prior art a plurality of measures whichhave the aim of producing and maintaining a load-bearing fluid pressurein the sealing gap and in this way of reliably separating the sealingfaces and thus stably establishing a narrow sealing gap. These measurescan be divided into the terms "hydrostatic" and "hydrodynamic" gappressure production. In the case of hydrostatic gap pressure production,measures are taken which alter the average value of the pressuredecreasing in the sealing gap from the pressure level in the space to besealed to the pressure level of the surrounding space. In thehydrodynamic gap pressure production, measures are taken as a result ofwhich the fluid which is entrained by the sealing face of the rotatingsealing ring in the sealing gap is accumulated at local gap-narrowinglocations, as a result of which the fluid pressure is increased, as inthe case of a hydrodynamic sliding bearing. However, an increase in thegap pressure has a disadvantage which is considerable from a sealingtechnology point of view, namely an increase in the sealing gap with theconsequence of an increase, often to a considerable extent, of leakage.With regard to environmental protection, however, there is nowadays ageneral wish to reduce leakage drastically and reliably in all slidingring seals which seal "problem fluids". In order to stem leakage fromhydrodynamically lubricated sliding ring seals, there are in accordancewith the prior art special constructions, in which the fluid flowpenetrating from the space to be sealed into the sealing gap is guidedby means of particular structuring of the sealing faces such that someof it flows back into the said space. Disadvantages of knownconstructions having this mode of operation are their structure, whichis complicated from a production point of view, the relatively largeradial width of the sealing faces which is necessary because ofproduction of the structures, and the fact that the depressions are opento the low-pressure side, as a result of which in principle leakageoccurs with certain structural types when the shaft is at a standstilland there is a risk with other structural types that even smalldeformations of the sealing faces result in considerable leakage. Insome constructions, the fluid is entrained in the wrong direction inpartial regions of the sealing edge and leakage is thus produced.Another disadvantage of known constructions is the fact that theirreturn action only functions in one direction of rotation of the shaft.Finally, there are also known sliding ring seals in which spiral groovespump fluid out of the space on the low-pressure side into the space tobe sealed. However, this property goes against the object of the presentinvention.

For a number of reasons of sealing technology, not least to reduce theenergy loss caused by friction, modern sliding ring seals have verynarrow sliding faces, with a radial width of two millimeters or less.The gap height of a sliding ring seal which is established in operation,the axial spacing between the sealing faces, is, from the point of viewof avoiding leakage, most favourable when it is not substantiallygreater than the remaining unevenness of the sealing faces which havebeen lapped plane. The gap heights are thus generally in the order ofmagnitude of a micrometer. Hydrodynamically acting depressions in thesliding faces function as pressure-producing or as returning structuresto the optimum only if their depth is of the same order of magnitude asthe height of the sealing gap surrounding them.

There thus arise the basic objects, in the case of sliding ring seals,in particular those with a small sliding face width, first of preventingwear and overheating of the sealing faces by means of hydrodynamiclubrication, second of returning hydrodynamically to the first space tobe sealed the fluid which has penetrated into the sealing gap, and thirdof keeping leakage as small as possible when the shaft is at astandstill. Here, it is desirable for the sealing parts which achievethe objects to be capable of being produced reliably and economicallyand for them to function as far as possible equally in both directionsof rotation of the shaft. In cases where a respective fluid is locatedin the space to be sealed and in the surrounding space, and thetwo--similar or different--fluids have to be kept separate from oneanother reliably, there is a desire to convey the fluid which hasrespectively penetrated into the sealing gap from one of the two spacesback into the same space, and this function should as far as possiblealso be effective in both directions of rotation of the shaft.

These objects are achieved by means of depressions which are structuredin accordance with the invention and which are made in at least one ofthe radial sealing faces of the sliding ring seal. A sliding ring sealfor sealing the place at which a revolving shaft passes through a wallwhich separates a sealed space containing the fluid to be sealed from asecond space, a higher pressure generally prevailing in the sealed spacethan in the second space, has a first sealing ring, which is heldnon-rotatably against the wall and is sealed off with respect theretoand which has a planar first end face lying radially with respect to theshaft axis and delimited by an outer edge and an inner edge, and asecond sealing ring, which is held non-rotatably against the shaft andis sealed off with respect thereto and which has a planar second endface lying radially with respect to the shaft axis and delimited by anouter edge and an inner edge. The two end faces touch each other whenthe shaft is stationary and form a narrow sealing gap when the shaftrotates. One of the sealing rings is movable in the direction of theshaft axis and can be pressed against the other sealing ring. Generally,the pressure is effected by means of spring force and by the action ofthe overpressure prevailing in the sealed space.

To describe the inventive features of the sealing ring seal, first thefollowing terms are defined: a sealed space 31, a second space 32, asealing zone 35, two delimitation circles, a sealing circle 33, a zonecircle 34, a sealing zone width B, a centre circle 36, a first radialline 116, a second radial line 115, a return point 46, a sealing section411, a zone section 412, a return circle 461, a first reference face F1and a second reference face F2.

The space in which the fluid to be sealed is located is the sealed space31. The surrounding space, which is separated from the sealed space bythe sealing gap 13, is designated second space 32. The annular sealingzone 35 is the zone which is constantly covered by both end faces 113,213 of the sealing rings 11, 21 during rotation of the shaft. Thesealing zone is bounded by two delimitation circles whereof the centrepoints lie on the shaft axis 114. The radius of one of the twodelimitation circles is equal to the spacing between the shaft axis andthe point which is closest to the shaft axis of one of the outer edges111, 211 of the sealing rings. The radius of the other delimitationcircle is equal to the spacing between the shaft axis and the pointwhich is furthest from the shaft axis of one of the inner edges 112,212. The delimitation circle which is closer to the sealed space isdesignated the sealing circle 33, and the other is designated the zonecircle 34. Generally, the outer edges and the inner edges of the endfaces of the two sealing rings are circles. In this case, the sealingzone is located between the respectively largest inner edge and therespectively smallest outer edge of one of the two sealing rings. Thesealing zone width B is the spacing between the two delimitationcircles. The centre circle 36 is concentric with respect to thedelimitation circles, and its radius is equal to the arithmetic mean ofthe radii of the delimitation circles.

In at least one of the sealing rings a plurality of depressions 4 aremade from the end face thereof within the sealing zone 35, eachdepression having an edge 41 which is endless: on the end face. A radialline 115 intersecting the shaft axis touches the edge of the depressionon the one side; a radial line 116 touches the edge of the depression onthe other side. The radial lines therefore enclose the depression. Bothradial lines 115, 116 lie in the plane of the end face. Here, eachradial line can touch the edge of the depression at a single touchingpoint or at a plurality of touching points. However, there is on each ofthe two radial lines 115, 116 a respective touching point 45, 46 whichis closest to the sealing circle. These two touching points 45, 46divide the edge of the depression into two edge sections. The edgesection facing the sealing circle is the sealing section 411, and theother is the zone section 412. If the two touching points 45, 46 are notat the same spacing from the sealing circle, then the touching pointwhich has the smallest spacing from the sealing circle in absolute termsis designated the return point 46 and the radial line on which thereturn point 46 is located is designated the first radial line 116. Areturn point 46 has the spacing A from the sealing circle. The othertouching point 45 lies on the second radial line 115. The circle whereofthe centre point lies on the shaft axis and which passes through thereturn point 46 is called the return circle 461. If both touching points45, 46 are at the same spacing from the sealing circle, there are tworeturn points. In particular, if the depression 4 is mirror-symmetricalin relation to a radial and thus both touching points 45, 46 are at thesame spacing from the sealing circle, then consequently the returncircle passes through both touching points 45, 46.

The first reference face F1 is bounded by the return circle 461, thesealing section 411 and the radial line 115 intersecting the othertouching point 45. The area of the first reference face F1 is calculatednegatively where the sealing section 411 lies between the sealing circle33 and the return circle 461. The area of the first reference face F1 iscalculated positively where the return circle 461 lies between thesealing circle 33 and the sealing section 411. The second reference faceF2 is bounded by the return circle 461, the zone section 412 and thesecond radial line 115, and its area is calculated positively. Theconnection line between the point of intersection 117 of the end faceplane and the shaft axis, and any point 40 of the zone section 412 isdesignated the radius vector 110.

According to the invention, all the stated objects are together achievedby means of the depressions 4 made in the end faces in that their edgeslie completely within the sealing zone, in the depressions theentraining action of the rotating sliding face bringing the fluid asclose as possible to the sealing circle and at the same time putting ithydrodynamically under higher pressure so that the fluid flows back intothe sealed space at a small flow resistance, in accordance with theinvention the ratio of the spacing A from the sealing zone width B beingin the range 0.001≦(A/B)≦0.2, as a result of which the return point hasa very small spacing A from the sealing circle, and at the same time theratio of the first reference face to the second reference face of eachdepression being in the range -0.3≦(F1/F2)≦+0.9, as a result of whichthe fluid within the depression is guided in functionally favourablemanner to the return point. The range of A/B takes into account the spanof the radial sealing zone widths B which are usual in practice.

The arrangement, known per se, of hydrodynamically active depressionswithin the sealing zone and without connection to the sealed space hasthe advantage that when the shaft is at a standstill a lower pressureprevails in the depressions than in the sealed space. In contrast toknown depressions which have a return capability and which are connectedto the second space, the arrangement according to the invention of thedepressions which have a return capability has the essential advantagethat the very narrow sealing gap, which is formed only by the smallunevennesses of the end faces when the shaft is at a standstill, islocated between the depressions and the second space. As a result, therisk of leakage when the shaft is at a standstill is hardly greater withthe sliding ring seal according to the invention than with a slidingring seal without depressions and having the same sealing zone width B.The depressions are preferably arranged between the sealing circle andthe centre circle so as to make the flow resistance between the zonesection of a depression and the second space as large as possible as aresult.

A spacing A different from zero must be present so that a high pressure,which favours both the return action and the lubrication of the slidingfaces, can be produced hydrodynamically in the region of the returnpoint 46 by the entraining action of the rotating sliding face. Thespacing A is at most 0.5 mm, and preferably smaller than 0.1 mm. Withwell centred and precisely machined sealing rings, for example, aspacing A of approximately 10 micrometers can be realized and producesan excellent return action. A good compromise between manufacturingexpense and return action is achieved in the range A=50 to 100micrometers.

In order to avoid increased inward flow from the sealed space directlyinto a depression with return capability according to the invention,preferably no point on the sealing section 411 is closer to the sealingcircle 33 than the return point 46, as a result of which F1 generallyhas a positive sign and consequently preferably 0≦(F1/F2)≦0.9. Aparticularly favourable return action is produced if, on average, thefluid in the depression is brought to the return circle at a smallangle. For this purpose the ratio is preferably in the range0.1≦(F1/F2)≦0.5.

If the sealing circle is larger than the zone circle and the sealedspace thus surrounds the sliding ring seal, with a small spacing Aaccording to the invention of the return point from the sealing circlethe return action is particularly favourable if according to theinvention the sealing section is shorter than the zone section. Anequally favourable return action in both directions of rotation of theshaft is achieved according to the invention in that the depressions aremirror-symmetrical in relation to a radial. A favourable return actionis also achieved in that the zone section is shaped such that the radiusvector rotates in at most one direction when moving over the zonesection. This means that at the zone section recessed dents andprojecting tongues of the depression are eliminated and that thus in theregion of the zone section--other than at the sole projecting place atthe return point--there is no local excessive increase in pressure withits attendant increased emergence of fluid from the depression into thesealing gap.

Preferably, a depression according to the invention comprises at leasttwo hollows of different lengths, the respectively longer hollow havinga smaller spacing from the sealing circle than any smaller hollows, thatthe hollows adjoin one another along parts of their longitudinal edgessuch that the cavities formed by the hollows and the constant sealingface merge with one another. By hollows there is substantially meant anelongate depression which has substantially a right-angledcross-section. The hollows are arranged substantially such that theirlongitudinal extent runs chiefly tangentially, that is to say in thedirection of the tangent on a circle lying on the sealing face andhaving its centrepoint on the shaft axis. At least one of the ends ofthe longest hollow on which the return point lies has, according to theinvention, a small spacing of less than 0.5 mm from the sealing circle.The result of each of these measures is that the fluid which is in thehollow and is entrained by the sealing face, which rotates relative tothe sealing face provided with the depressions, accumulates at the rearend of a hollow--as seen in the direction of entrainment--and overflowsinto the adjacent hollow. The arrangement of the hollows relative to thesealed space has the effect that the fluid, in the manner of a cascade,finally reaches the hollow which is closest to the first space. Thefluid entrained in this hollow in the longitudinal direction thereof isaccumulated towards the end of this hollow, where there is no furtheradjacent hollow. As a result and depending on the rate of entrainment,the viscosity and depth of the hollow, the pressure of the fluid isincreased considerably towards the end of this hollow. This end has avery small spacing from the sealing circle, in accordance with theinvention. As a result, the distance and thus also the flow resistancebetween the end of this hollow and the sealed space is small within thesealing gap, as a result of which a large proportion of the fluidflowing out of this hollow flows into the sealed space.

Preferably, the mutually adjoining hollows are of different depths suchthat the longest hollow has the smallest depth and the shortest hollowhas the greatest depth, the cavities formed by the hollows and theconstant sealing face each merging with a step in the regions in whichhollows adjoin one another. Preferably, in a region in which two hollowsadjoin one another, the respectively less deep hollow lies closer to thesealing circle, or in other words, as seen from the sealed space, arespectively more distant hollow is deeper than a less distant one.Exceptions to this rule, which is preferably to be adhered to, areappropriate if it appears favourable to provide deeper hollows inbetween for the purpose of collecting and storing foreign bodies whichhave penetrated into the sealing gap or abrasion, reaction,precipitation or coking products which have arisen in the gap.

The hollow having the smallest depth is preferably between 0.2micrometers and 5 micrometers deep, and the height of a step--equal tothe difference in depths of two mutually adjoining hollows--ispreferably between 0.2 micrometers and 5 micrometers. The width and thedepth of individual hollows can be variable in the longitudinaldirection of the hollow. Preferably, the width of a hollow is between0.05 and 0.2 millimeters. Preferably, the depth of at least one of thehollows, as seen in its longitudinal direction, lessens towards at leastone of its ends. Preferably, the depth of the hollow whereof the end isclosest to the sealing circle lessens towards this end. As a result, thepressure at the end of this hollow becomes particularly great and thereturn action is particularly intensive and favourable.

Preferably, at least one longitudinal edge of at least one hollow iscurved, the centre point of the curvature lying on the side of thesealed space. This embodiment is particularly advantageous if thesmaller of the two delimitation circles is the sealing circle. As aresult of the curvature of at least the hollow lying closest to the gapedge, the effect in this case is that at least one end of this hollowhas a very small spacing A from the sealing circle. In anotherfavourable embodiment of the sliding ring seal according to theinvention, the longitudinal edges of the hollows are straight lineswhich form a minimum angle α of preferably between 70° and 90° with aradial drawn through any point on a longitudinal edge. In a particularlyadvantageous embodiment which is suitable for both directions ofrotation of the shaft, the hollows are arranged to be mirror-symmetricalin relation to a radial.

In the case of a further type of the sliding ring seal according to theinvention, the edge sections of the depressions are polygonal figurescomprising straight and/or curved sections. In the case of a slidingring seal which is acted upon by pressure from the outside, in whichtherefore the sealing circle is larger than the zone circle, the sealingsection is preferably a single straight line and the zone section is acurve or a polygonal figure comprising at least two straight lines. Inan embodiment which is particularly favourable for manufacturing, andwhich is produced for example by an end-side incision of acircular-cylindrical tool which is set with its cylinder axis oblique inrelation to the end face, the edge of the depression has the shape of anellipse section whereof the chord is the sealing section. In a furtherpreferable embodiment, the edge of the depression has the shape of atriangle whereof the longest side is the sealing section. Preferably,the depth of the depressions is variable in such a way that they havethe least depth in the region of their sealing section. Preferably, thebase of the depressions is formed by a planar face inclined toward theend face. The maximum depth t of the depression is preferably between 1and 10 micrometers. These preferable edge shapes--ellipse section ortriangle--are again preferably mirror-symmetrical in relation to aradial, as a result of which they have the same return action in bothdirections of rotation of the shaft. If, when using depressions having amirror-symmetrical edge, a somewhat differing conveying action isdesirable with anticlockwise and clockwise movement of the shaft, thenthe chord or the longest triangle side forms an angle different from90°, preferably between 70° and 89°, with a radial drawn through itscentre.

In order to hydrodynamically lubricate the sealing faces and tostabilize the sealing gap, preferably, in addition to the depressionshaving return capability, in a manner known per se in the end face of atleast one sealing ring there are made additional depressions whichextend radially at least as far as the sealing circle, so that duringthe relative rotation of the two sealing rings the cavities formed bythe additional depressions together with the end face of the othersealing ring are at least sometimes connected to the sealed space.According to the invention, an additional depression is preferablybetween 1 micrometer and 20 micrometers deep. An additional depression,in conjunction with the definition of the sealing zone, is a part of theend face in which the additional depression is made, that is to say theposition of the delimitation circles is not altered by the existence ofadditional depressions. In order to maintain an advantageous symmetricaldistribution of the hydrodynamic fluid pressure over the sealingsurface, preferably at least two additional depressions are arranged atthe same spacing from the shaft axis and in each case with the sameangular spacing on the periphery. Preferably, at least one additionaldepression is arranged between two neighbouring depressions having areturn capability according to the invention.

Finally, for the purpose of separating two different fluids whichsurround the sealing rings respectively on the outside and on theinside, the depressions 4 are in accordance with the invention arrangedsuch that each fluid is separately conveyed back into the space fromwhich it flowed into the gap. In this case, in accordance with thedefinition, the second space 32 is also a sealed space and consequentlyboth delimitation circles are, in accordance with the definition,sealing circles. At the same time, at a small spacing from the secondsealing circle 34 there is defined a second return circle 462 on whichthe return points 46 of some of the depressions lie.

So that the depressions, which according to the invention are onlyfractions of a micrometer to a few micrometers deep, and additionaldepressions cannot disappear as a result of wear of the sealing face, inaccordance with the invention they are made in a sealing ring of veryhard, wear-resistant material. Preferably, the sliding rings of thesliding ring seal according to the invention in which depressions aremade are of ceramic material. Because of the high wear resistance, thechemical resistance and the good thermal conductivity of siliconcarbide, this material is preferably used for sliding rings having thereturn structures according to the invention.

Depressions having a very small depth of fractions of a micrometer to afew micrometers for the purpose of optimum return action according tothe invention, are made in the sealing rings preferably by means oflaser beam or electron beam. In a known machining process, comparativelydeep structures are made in unsintered "starting sheets" of ceramicmaterials by means of laser beams. In the case of the sliding ring sealaccording to the invention, on the other hand, the depressions accordingto the invention are made in the hard material of the sealing ring. Inparticular, the depressions according to the invention are made, in theceramic materials which are preferably used in the prior art for slidingring seals, according to the invention in the sintered, that is to sayhard sealing rings whereof machining has already been effected bylapping plane the sealing faces. Because of the particular advantage ofa direct high-precision material removal by the dissociation of chemicalcompounds using the high photon energy of very short-wave excimer laserbeams, the depressions, which according to the invention are very small,in extremely hard materials of the sealing rings are preferably madeaccording to the invention by means of excimer laser. Preferably, thedepressions are made by means of excimer laser after the final machiningof the sealing rings, in the sealing face which has already been lappedplane. Preferably, at least some of the depressions are made by repeatedsuccessive laser irradiation of the projected surface or parts of theprojected surface of the depressions.

Preferably, when manufacturing elongate, hollow-shaped depressions,regions which succeed one another in the longitudinal direction of thehollow are irradiated in overlapping manner, as a result of which somepartial regions are irradiated more frequently and are consequentlydeeper than the regions adjoining them. In accordance with theinvention, this is done with the purpose of in all cases avoidingleaving a web when machining at the transition from one hollow toanother. A web of this type would block the flow of the fluid in thedepression and thus considerably impair the return action of thedepressions. For the same reason, hollows which are mutually adjoiningat their longitudinal sides are preferably irradiated in overlappingmanner, as a result of which a deeper incision is produced at thetransition from one hollow to another.

The invention will be explained below with reference to a series ofexample embodiments illustrated in the drawings, in which:

FIG. 1 shows a longitudinal section through a sliding ring seal,

FIG. 1a shows a partial view of the end face, with the illustration inprinciple and the designations of the edge of the depression of thesliding ring seal according to the invention,

FIG. 1b shows a partial view of the end face, with the illustration inprinciple of the return point and of the return circle of the slidingring seal according to the invention,

FIG. 1c shows two partial views of the end face, with the illustrationin principle of the first reference face of the sliding ring sealaccording to the invention,

FIG. 1d shows a partial view of the end face, with the illustration inprinciple of the second reference face of the sliding ring sealaccording to the invention,

FIG. 2 shows the view of sectors of a total of 8 embodiments of the edgeof the depressions of the sliding ring seal according to the invention,

FIG. 3 shows, in two partial views, the end faces with two differentembodiments of the depressions of the sliding ring seal according to theinvention, with additional depressions,

FIG. 4 shows the explanation of the flow through hollow-shapeddepressions and additional depressions of the sliding ring sealaccording to the invention,

FIG. 5 shows, in perspective illustration, a section through a sealingring of the sliding ring seal according to the invention, havinghollow-shaped depressions.

FIG. 6 shows, in perspective illustration, a section through a sealingring of the sliding ring seal according to the invention, havingdepressions incised obliquely and having an elliptical edge,

FIG. 7 shows, in two partial views, the end faces of two differentembodiments having depressions on the inside and on the outside of thesliding ring seal according to the invention, for the separation of twofluids,

FIG. 8 shows a partial view of the end face of a sliding ring sealaccording to the invention, having depressions on the inside and on theoutside, for the separation of two fluids, and

FIG. 9 shows the explanation of the flow through the depressions andadditional depressions of a sliding ring seal according to theinvention, having depressions on the inside and on the outside, for theseparation of two fluids.

The arrangement which is illustrated by way of example in FIG. 1contains the basic elements and features of a sliding ring seal whichseals the place at which a revolving shaft 1 passes from a sealed space31 through a wall 2 into a second space 32, namely: an axially movablefirst sealing ring 21 which is held against a wall by means of arotation-prevention element 200, is sealed therefrom by a static sealingelement 20 and has an end face 213; a second sealing ring 11 which isheld against the shaft by means of a rotation-prevention element 100, issealed off therefrom by a static sealing element 10 and has an end face113; a depression 4; a spring 23 acting axially on the first sealingring; and with a sealing gap 13 which is established between the endfaces in operation.

FIG. 1a shows a partial view of the end face of the sealing ring 11according to the invention from FIG. 1, with an illustration inprinciple of a depression 4 made in the sealing ring. The part of theend face 113 which is shown shaded in in FIG. 1a is the sealing zone 35.It is the zone which is covered by both end faces at all times when theshaft rotates, and it lies between the sealing circle 33 and the zonecircle 34. If the outer edges and inner edges of the sealing rings aremade to be circular and concentric to the shaft axis, then the sealingcircle 33 is identical to the smaller of the two outer edges 111, 211,and the zone circle is identical to the larger of the two inner edges112, 212. The centre circle 36 lies in the centre of the sealing zone.The edge 41 of the depression is touched on the left by the first radialline 116, at the touching point 46. On the right, the second radial line115 touches the edge along a straight section of the edge. The point onthe part of the edge which is touched in a straight line which has thesmallest spacing of all the points of this straight section from thesealing circle 33 is by definition the other touching point 45. Of thetwo touching points, the touching point 46 has the smallest spacing fromthe sealing circle 33 and is thus by definition the return point 46.Between the touching points 45 and 46, the sealing section 411 extendson the side of the sealing circle 33, and the zone section 412 extendson the side of the zone circle 34. The radius vector 110 is theconnection line between the point of intersection 117 of the sealingface plane and the shaft axis and any point 40 on the zone section 412.

In the sealing arrangement shown in FIGS. 1 and 1a, the sealed space 31lies, by way of example, outside the outer edges of the sealing rings11, 21, and the second space is within the inner edges thereof. It goeswithout saying that the sealed space can also be on the inside andconsequently the second space on the outside. In the latter case, thedesignations regarding the sealing circle and the zone circle in FIG. 1ahave to be interchanged. The sealing circle in this case lies on theinside of the sealing zone, and according to the invention thedepression is again arranged such that the return point 46 has a verysmall spacing A from the sealing circle.

FIG. 1b shows another shape of a depression 4. The first radial line 116passes through the return point 46, as does the return circle 461, whichhas the spacing A from the sealing circle 33. The spacing from thesealing circle 33 to the zone circle 34 is designated the sealing zonewidth B. The second radial line 115 passes through the second touchingpoint 45. The edge of the depression has the sealing section 411 and thezone section 412.

FIG. 1c shows at the top the first reference face F1, which is enclosedby the return circle 461, the sealing section 411 and the second radialline 115. FIG. 1c shows at the bottom another shape of the edge of adepression, in which the sealing section intersects the return circlerepeatedly. As a result, by definition positive and negative portions ofthe reference face F1 are produced.

FIG. 1d shows the second reference face F2, which is enclosed by thereturn circle 461, the zone section 412 and the second radial line 115.FIGS. 1c and 1d illustrate the area ratio F1/F2 and--in conjunction withthe feature according to the invention that the width, as measured inthe radial direction, of a depression in the vicinity of the returnpoint is smaller than in the central region of the depression--shows therelationship between the shape of the depression and the return action.

FIG. 2 shows, in the FIGS. 2a to 2h which are constituents thereof, theviews of a total of 8 embodiments of the depression 4 of the slidingring seal according to the invention. For all the examples of FIG. 2, itis assumed that the sealed space 31 lies on the outside. This isgenerally the case with sliding ring seals. The features according tothe invention are, however, readily applicable even to a sliding ringseal in which the sealed space 31 lies on the inside and the secondspace 32 on the outside. FIG. 2a shows a general basic shape having theedge sections 411 and 412, which are determined by the touching points45 and 46 of the radial lines touching on either side. FIG. 2b shows amodified basic shape. The edge contours in accordance with FIGS. 2c, 2d,2e and 2f are triangles. In FIG. 2d, the zone section extends inaccordance with the definition around the inner corner to the point 45,since the shortest side of the triangle is directed radially. FIG. 2gshows an edge contour which tapers very sharply by way of the zonesection 412. FIG. 2h shows a depression having an edge which has theshape of a circle segment or an ellipse segment. The embodiments inaccordance with FIGS. 2f, 2g and 2h are mirror-symmetrical to a radial118 and thus demonstrate the same properties in both directions ofrotation of the shaft. In all the embodiments of the edge contour of thedepressions shown in FIG. 2, according to the invention at least one ofthe touching points lies very close to the sealing circle 33.

FIG. 3 shows, in two partial views, the constant sealing zones 35 of theend faces 113 and 213 of two different embodiments, namely that on theright having depressions 43 whereof the edge is a circle or ellipsesegment which is mirror-symmetrical to the radial 118, and that on theleft having mirror-symmetrical depressions 42 which comprise a pluralityof mutually adjoining narrow hollows. Additional depressions 51 whichare connected to the first sealed space 31, which in this case lies onthe outside, are arranged between the depressions.

FIG. 4 explains the flow through the depressions and additionaldepressions of the sliding ring seal according to the invention, usingthe example of flow through hollow-shaped mutually adjoiningmirror-symmetrical depressions 422. Fluid from the sealed space 31reaches the additional depression 51 which is open towards the sealingedge, and this fluid is entrained by the end face of the other sealingring, which in relation to the additional depression slides over it, outof the additional depression into the sealing gap. There, it isentrained further over the edges of the hollows of the depression intothe hollows 421,422,423 and 424. At the same time, fluid flows as aresult of capillary action and in some cases as a result of an excesspressure in the sealed space 31 radially by way of the sealing circle 33inwards into the sealing gap and into the hollows. As a result of axialfluctuations in the gap walls, fluid is additionally squashed into thedepression, stripped off and again accumulated in the hollows byentraining action at the ends of the hollows. At the end of arespectively shorter hollow the accumulated fluid escapes laterally intothe adjacent longer hollow and from there is entrained further and thuspasses in the manner of a cascade finally into the longest hollow 421.At the end 420 of this hollow, which according to the invention is veryshallow, there is produced a relatively high hydrodynamic pressure whichcan quite easily be very much greater than the pressure in the sealedspace 31. Since the end 420 of the longest hollow 421 lies very close tothe sealing circle 33, in accordance with the invention, the flowresistance in the gap between the end 420 of the hollow 421 and thesealed space 31 is relatively small, and a large proportion of the fluidflow which is "accumulated" and diverted by the depression passes backto the first space by way of the sealing circle 33.

FIG. 5 shows, in perspective illustration, a section through a sealingring of the sliding ring seal according to the invention, havinghollow-shaped depressions 421, 422, 423, which according to theinvention are preferably produced by means of laser beams. The depth hof the shallowest and at the same time longest hollow 421 adopts,towards its end 420, an even smaller value in the region 453, as aresult of which the pressure at the end of the hollow becomes extremelyhigh. The edge of the hollow 421 is part of the sealing edge 411. Thehollow 421 has the width b. The step Δh between the hollows isapproximately as large as the depth of the shallowest hollow. Thedeepest hollow 423 has the depth t. When producing the elongatedepressions, successive regions are irradiated in overlapping manner inthe longitudinal direction of the hollows, as a result of which somepartial regions 452 are deeper than regions of the hollows adjoiningthem. Similarly, hollows adjoining one another at their longitudinalsides are preferably irradiated in overlapping manner, as a result ofwhich deeper incisions 451 are produced at the transition from onehollow to another.

FIG. 6 shows, in perspective illustration, a section through a sealingring of the sliding ring seal according to the invention, havingdepressions which are incised obliquely and which have by way of anexample an elliptical zone section 412. On the inside the depression isdelimited by the, for example, planar face 431, and has the depth t atthe deepest point. Here, the cross-section of the depression is doublyreduced in the direction of entrainment towards the end 430 inaccordance with the invention, namely on the one hand the radial widthand on the other hand the depth are reduced. As a result, a particularlygreat build-up of hydrodynamic pressure which is active for gapformation and for the return of the fluid is produced with anadvantageous effect at the return point.

FIG. 7 shows, in two partial views, the constant sealing zones of twodifferent embodiments of the sliding ring seal according to theinvention as suitable for the separating sealing of two fluids,respectively located in the space 31 and in the space 32. Both insideand indeed outside the centre circle 36, depressions 4 which are in eachcase mirror-symmetrical to a radial made in the end faces. Between thedepressions, additional depressions 51 are made on the outside andfurther additional depressions 52 are made on the inside, in each caseconnected to the adjoining spaces 31 and 32 respectively. Thedepressions 4 convey the fluid which comes into the gap from therespectively adjoining space by way of the respective delimitationcircle--which is consequently a sealing circle--back into the samespace.

FIG. 8 illustrates the flow through the depressions and additionaldepressions between the end faces of the sliding ring seal according tothe invention, shown in FIG. 7 in the partial view on the left. Thecourse of the flow is analogous to the course explained in FIG. 4. Onthe inside, hollow-shaped depressions 4 which have hollows which are ineach case curved towards the delimitation circle are made in the endfaces. As a result, it is possible in accordance with the invention tobring the ends of the hollow which is closest to the inner sealingcircle 34 very close to the sealing circle 34. On the outside, the shapeand function of the hollows of the depression 4 corresponds to theembodiment explained with reference to FIG. 4.

Finally, FIG. 9 shows a partial view of the constant sealing zone of asliding ring seal according to the invention for the purpose of theseparating sealing of two fluids which are respectively located in thespace 31 and in the space 32. Both inside and outside the centre circle36 there are made depressions 4 in the end face. The return point 46 ofthe outer depressions lies on an outer return circle 461, which has thesmall spacing A from the outer sealing circle 33. The return point 46 ofthe inner depressions lies on an inner return circle 462, which has thesmall spacing A from the inner sealing circle 34. The spacing betweenthe two sealing circles is here the sealing zone width B. Between thedepressions there are made additional depressions 51 on the outside andfurther additional depressions 52 on the inside, which are in each caseconnected to the adjoining spaces 31 and 32 respectively. Since in thisembodiment only one of the touching points of the radial lines 115, 116,namely in each case the return point 46, lies on the respective returncircle, this sliding ring seal has a return action only in one directionof rotation of the shaft. In the other direction of rotation of theshaft, in this case the fluid would be guided in the depressions, ineach case radially towards the centre circle, as far as the touchingpoint 45, and would flow out of the depression into the sealing gaprelatively far away from the respective sealing circle. As a result,although the sliding surfaces would be hydrodynamically lubricated, thesealing action would be poor.

I claim:
 1. Sliding ring seal for sealing the place at which a revolvingshaft (1) passes through a wall (2) which separates a sealed space (31)containing a fluid from a second space (32), a higher pressure generallyprevailing in the sealed space than in the second space, and the slidingring seal having a first sealing ring (21), which is held non-rotatablyagainst the wall and is sealed off with respect thereto and which has aplanar first end face (213) lying radially with respect to the shaftaxis (114) and delimited by an outer edge (211) and an inner edge (212),that the sliding ring seal furthermore has a second sealing ring (11),which is held non-rotatably against the shaft and is sealed off withrespect thereto and which has a planar second end face (113) lyingradially with respect to the shaft axis and delimited by an outer edge(111) and an inner edge (112), one of the sealing rings being movable inthe direction of the shaft axis and being pressable against the othersealing ring, and the two end faces touching each other when the shaftis stationary and forming a narrow sealing gap (13) when the shaftrotates, the region of the sealing gap which is covered by both endfaces at all times when the shaft rotates being designated a sealingzone (35), the sealing zone being enclosed by two delimitation circleswhereof the centre point of each lies on the shaft axis and the radiusof one delimitation circle being equal to the distance between the shaftaxis and the point closest thereto of one of the outer edges (111, 211)and the radius of the other delimitation circle being equal to thedistance between the shaft axis and the point furthest therefrom of oneof the inner edges (112, 212), and the delimitation circle which iscloser to the sealed space (31) being designated a sealing circle (33),and the delimitation circle which is closer to the second space (32)being designated a zone circle (34), that the distance between thedelimitation circles is designated the sealing zone width (B), and thatin at least one of the sealing rings a plurality of depression (4) aremade in the end face (113,213) thereof, a single row of depressionsbeing disposed adjacent at least one of the sealing and zone circles,that each depression has an edge (41) which is endless on the end faceand which is within the sealing zone (35), and that two edge sectionsare defined by the fact that the edge of each depression is touched oneach side by a respective one radial line (115, 116) intersecting theshaft axis and lying in the plane of the end face, that the radial linestherefore enclose the depression, two touching points (45 and 46) eachlying on one radial line which have in each case the smallest distancefrom the sealing circle of all the touching points lying on the sameradial line dividing the edge into two edge sections and the edgesection facing the sealing circle being designated a sealing section(411) and the remaining edge being designated a zone section (412), thatof the two touching points (45 and 46) the one which has the smallestdistance from the sealing circle is designated a return point (46), theradial line passing through the return point being designated a firstradial line (116) and the other being designated a second radial line(115), that furthermore a return circle (461)is defined which passesthrough the return point (46) and whereof the centre point lies on theshaft axis, that a first reference face (F1) is defined which is boundedby the return circle 461, the sealing section (411) and the secondradial line (115) and whereof the area is assigned a negative valuewhere the sealing section 411 lies between the sealing circle (33) andthe return circle (461) and a positive value where the return circle(461) lies between the sealing circle (33) and the sealing section(411), and that a second reference face (F2) is defined which is boundedby the return circle (461), the zone section (412) and the second radialline (115) and whereof the area is calculated positively, characterizedin that at least one of the touching points has a small spacing (A) fromthe sealing circle which is between 0.1% and 20% of the sealing zonewidth (B), wherein the ratio of A/B is in the range between 0.001 and0.2 and in that the ratio of the first reference face (F1) to the secondreference face (F2) is in the range between -0.3 and +0.9.
 2. Slidingring seal according to claim 1, characterized in that the small spacing(A) is between 1% and 10% of the sealing zone width B, and in that theratio of the first reference face (F1) to the second reference face (F2)is in the range between 0 and +0.9.
 3. Sliding ring seal according toclaim 2, characterized in that the ratio of the first reference face(F1) to the second reference face (F2) is in the range between +0.1 and+0.9.
 4. Sliding ring seal according to claim 3, characterized in thatthe small spacing (A) is at most 0.5 mm.
 5. Sliding ring seal accordingto claim 4, characterized in that the small spacing (A) is smaller than0.2 mm.
 6. Sliding ring seal according to claim 1, a centre circle (36)concentric with respect to the delimitation circles being defined,whereof the radius is equal to the arithmetic mean of the radii of thedelimitation circles, characterized in that the edge (41) of eachdepression (4) is between the sealing circle (33) and the centre circle(36).
 7. Sliding ring seal according to claim 1, characterized in thatthe edge (41) of a depression is mirror-symmetrical in relation to aradial line (118) and the return circle (461) consequently passesthrough both touching points (45 and 46).
 8. Sliding ring seal accordingto claim 1, characterized in that the maximum depth (t) of at least oneof the plurality of depressions is between 0.2 and 10 micrometers. 9.Sliding ring seal according to claim 8, characterized in that the baseof at least one of the plurality of the depressions is formed at leastin part by a planar face (431) inclined toward the end face (113, 213).10. Sliding ring seal according to claim 9, characterized in that thedepth of at least one of the plurality of depressions is smaller in thevicinity of at least one of the touching points (45, 46) than in thecentral region of the at least one of the plurality of depression. 11.Sliding ring seal according to claim 9, characterized in that the widthof at least one of the plurality of depressions as measured in theradial direction is smaller in the vicinity of at least one of thetouching points than in the central region of the at least one of theplurality of depressions.
 12. Sliding ring seal according to claim 1,characterized in that each of the plurality of depressions (4) comprisesat least two hollows (421, 422, 423) of different lengths, therespectively longer hollow having a smaller spacing from the sealingcircle (33) than any smaller hollows, in that the hollows adjoin oneanother along parts of their longitudinal edges such that the cavitiesformed by the hollows and the end face plane (113, 213) merge with oneanother and the hollows are arranged substantially such that theirlongitudinal extent runs chiefly tangentially.
 13. Sliding ring sealaccording to claim 1, characterized in that the edge of a depressioncomprises a polygonal figure having a straight portion.
 14. Sliding ringseal according to claim 1, characterized in that the sealing section(411) is a single straight line (413).
 15. Sliding ring seal accordingto claim 1, characterized in that the zone section (412) is a polygonalfigure comprising at least two straight lines.
 16. Sliding ring sealaccording to claim 1, the sealing circle (33) being larger than the zonecircle (34), characterized in that the sealing section (411) is shorterthan the zone section (412).
 17. Sliding ring seal according to claim 1,the connection line between the point of intersection (117) of the shaftaxis and the end face plane, and any point (40) of the zone section(412) being defined as a radius vector (110), characterized in that whenthe point (40) moves on the zone section (412) from one touching point(45) to the other touching point (46) the radius vector rotates in atmost one direction.
 18. Sliding ring seal according to claim 1, wherethe second space (32) also contains a fluid which has to be keptseparate from the sealed space (31), that is to say the second space isalso a sealed space and consequently the zone circle (34) is at the sametime a second sealing circle, a second return circle (462) being definedwhich has the small spacing (A) from the second sealing circle,characterized in that in the case of some of the depressions (4) thereturn point (46) lies on the second return circle (462).
 19. Slidingring seal according to claim 1, characterized in that at least in one ofthe end faces (113, 213) there are further included additionaldepressions (51, 52) which are between 1 micrometer and 20 micrometersdeep and extend radially at least as far as a sealing circle, so thatany said additional depression is connected at least sometimes to asealed space.
 20. Sliding ring seal according to claim 1, characterizedin that the ring in which depressions are made is of ceramic material.21. Sliding ring seal according to claim 12, characterized in that themutually adjoining hollows are of different depths such that the longesthollow (421) has the smallest depth and the shortest hollow (424) hasthe greatest depth, the cavitties formed by the hollows and the end faceplane (113, 213) each merging with a step in the regions in whichhollows adjoin one another.
 22. Sliding ring seal according to claim 21,characterized in that in a region in which two hollows adjoin oneanother, the respectively less deep hollow lies closer to the sealingcircle (33) than any deeper hollow.
 23. Sliding ring seal according toclaims 22, characterized in that the depth (h) of the shallowest hollow(421) is between 0.2 micrometers and 5 micrometers, and the height (Δh)of a step between two hollows is between 0.2 micrometers and 5micrometers.
 24. Sliding ring seal according to claims 23, characterizedin that the width (b) of a hollow is between 0.05 and 0.2 millimeters.25. Sliding ring seal according to claim 24, characterized in that thedepth of at least one hollow, as seen in its longitudinal direction,lessens towards at least one of the touching points (45, 46). 26.Sliding ring seal according to claims 12, characterized in that thelongitudinal edges of the hollows are straight lines.
 27. Sliding ringseal according to claim 12, characterized in that at least onelongitudinal edge of at least one hollow is curved, and the centre pointof the curvature is outside the sealing circle (33).
 28. Sliding ringseal according to claim 1, characterized in that the edge of adepression comprises a polygonal figure which has curved portions. 29.Sliding ring seal according to claim 19, characterized in that saidplurality of depressions and said additional depressions are made in thesealing ring by one of a laser beam and an electron beam.
 30. Slidingring seal according to claim 29, characterized in that the depressionsare made by means of the laser beam of an excimer laser.
 31. Slidingring seal according to claims 29, characterized in that at least some ofthe depressions are made by repeated successive irradiation of at leasta portion of the projected surface of the depressions.
 32. Sliding ringseal according claims 29, characterized in that mutually adjoiningregions of a depression are irradiated in overlapping manner, as aresult of which the partial regions irradiated in overlapping manner aredeeper than the regions adjoining them.
 33. Sliding ring seal accordingto claims 29, characterized in that a plurality of depressions areproduced simultaneously by simultaneous irradiation of a plurality oflocations on the sealing ring.
 34. Sliding ring seal according to claim20, characterized in that the depressions are made in the sealingsurface of the sintered hard ceramic ring which has already been lappedplane.
 35. Sliding ring seal according to claim 34, characterized inthat the ceramic material is silicon carbide.